Copolymers and films thereof

ABSTRACT

Novel copolymers comprise ethylene and alpha olefins having from 3 to 10 carbon atoms and which have
         (a) a density in the range 0.900 to 0.940   (b) Mw/Mn of 2-3.4   (c) I 21 /I 2  from 16 to 24   (d) activation energy of flow from 28 to 45 kJ/mol   (e) a ratio Ea(HMW)/Ea(LMW)&gt;1.1, and   (f) a ratio g′(HMW)/g′(LMW) from 0.85 to 0.95       

     The copolymers are particularly useful in film applications showing an excellent balance of processing, optical and mechanical properties. The novel polymers may suitably be prepared in the gas phase in the presence of metallocene complexes.

The application is a divisional of application Ser. No. 09/695,915,filed Oct. 26, 2000, now U.S. Pat. No. 6,642,339, which is acontinuation of International Application No. PCT/GB00/01611, filed Apr.26, 2000.

The present invention relates to copolymers of ethylene andalpha-olefins in particular to low density copolymers and also to filmsproduced from said copolymers.

In recent years there have been many advances in the production ofpolyolefin copolymers due to the introduction of metallocene catalysts.Metallocene catalysts offer the advantage of generally higher activitythan traditional Ziegler catalysts and are usually described ascatalysts which are single-site in nature. Because of their single-sitenature the polyolefin copolymers produced by metallocene catalysts oftenare quite uniform in their molecular structure. For example, incomparison to traditional Ziegler produced materials, they haverelatively narrow molecular weight distributions (MWD) and narrow ShortChain Branching Distribution (SCBD).

Although certain properties of metallocene products are enhanced bynarrow MWD, difficulties are often encountered in the processing ofthese materials into useful articles and films relative to Zieglerproduced materials. In addition, the uniform nature of the SCBD ofmetallocene produced materials does not readily permit certainstructures to be obtained.

Recently a number of patents have published directed to the preparationof films based on low density polyethylenes prepared using metallocenecatalyst compositions.

WO 94/14855 discloses linear low density polyethylene (LLDPE) filmsprepared using a metallocene, alumoxane and a carrier. The metallocenecomponent is typically a bis (cyclopentadienyl) zirconium complexexemplified by bis (n-butylcyclopentadienyl) zirconium dichloride and isused together with methyl alumoxane supported on silica. The LLDPE's aredescribed in the patent as having a narrow Mw/Mn of 2.5-3.0, a melt flowratio (MFR) of 15-25 and low zirconium residues.

WO 94/26816 also discloses films prepared from ethylene copolymershaving a narrow composition distribution. The copolymers are alsoprepared from traditional metallocenes (eg bis (1-methyl,3-n-butylcyclopentadienyl) zirconium dichloride and methylalumoxanedeposited on silica) and are also characterised in the patent as havinga narrow Mw/Mn values typically in the range 3-4 and in addition by avalue of Mz/Mw of less than 2.0.

However, it is recognised that the polymers produced from these types ofcatalyst system have deficiencies in processability due to their narrowMw/Mn. Various approaches have been proposed in order to overcome thisdeficiency. An effective method to regain processability in polymers ofnarrow Mw/Mn is by the use of certain catalysts which have the abilityto incorporate long chain branching (LCB) into the polymer molecularstructure. Such catalysts have been well described in the literature,illustrative examples being given in WO 93/08221 and EP-A-676421.

Furthermore, WO 97/44371 discloses polymers and films where long chainbranching is present, and the products have a particularly advantageousplacement of the comonomer within the polymer structure. Polymers areexemplified having both narrow and broad Mw/Mn, for example from 2.19 upto 6.0, and activation energy of flow, which is an indicator of LCB,from 7.39 to 19.2 kcal/mol (31.1 to 80.8 kJ/mol). However, there are noexamples of polymers of narrow Mw/Mn, for example less than 3.4, whichalso have a low or moderate amount of LCB, as indicated by an activationenergy of flow less than 11.1 kcal/mol (46.7 kJ/mol).

We have now found that it is possible to prepare copolymers of ethyleneand alpha-olefins having narrow Mw/Mn and low or moderate amounts ofLCB. These polymers are suitable for many applications which will beknown to those skilled in the art, but in particular are advantageousfor preparing films with an excellent balance of processing, optical andmechanical properties.

Thus, according to the present invention there is provided a copolymerof ethylene and an alpha olefin having 3 to 10 carbon atoms, saidpolymer having

-   -   (a) a density in the range 0.900 to 0.940    -   (b) an apparent Mw/Mn of 2-3.4    -   (c) I₂₁/I₂ from 16 to 24    -   (d) activation energy of flow from 28 to 45 kJ/mol    -   (e) a ratio Ea(HMW)/Ea(LMW) >1.1, and    -   (f) a ratio g′(HMW)/g′(LMW) from 0.85 to 0.95.

Preferred copolymers are those having

-   -   (a) a density in the range 0.900 to 0.940    -   (b) an apparent Mw/Mn in the range 2 to 3    -   (c) I₂₁/I₂ from 18-24    -   (d) activation energy of flow from 28 to 45 kJ/mol    -   (e) a ratio Ea(HMW)/Ea(LMW) >1.1, and    -   (f) a ratio g′(HMW)/g′(LMW) from 0.85 to 0.95.

Most preferred copolymers are those having

-   -   (a) a density in the range 0.900 to 0.940    -   (b) an apparent Mw/Mn in the range 2.5 to 3    -   (c) I₂₁/I₂ from 18-24    -   (d) activation energy of flow from 30 to 35 kJ/mol    -   (e) a ratio Ea(HMW)/Ea(LMW) >1.2, and    -   (f) a ratio g′(HMW)/g′(LMW) from 0.85 to 0.95.

By apparent Mw/Mn is meant a value of Mw/Mn uncorrected for long chainbranching.

The significance of the parameters Ea(HMW)/Ea(LMW) and g′(HMW)/g′(LMW)is described below. The experimental procedures for their measurementsare described later in the text.

The polymers contain an amount of LCB which is clearly visible bytechniques such as GPC/viscometry and flow activation energy. Thecontent of LCB is lower than reported in many earlier publications, butis still sufficient, when coupled with broadened Mw/Mn, to give improvedprocessability compared to linear polymers of narrow MWD (Mw/Mn lessthan about 3), which do not contain LCB.

For the measurement of LCB, we have found that the most usefultechniques are those which have a particular sensitivity to the presenceof LCB in the high molecular weight chains. For these high molecularweight molecules, the physical effects of LCB on the solution and meltproperties of the polymer are maximised. Hence detection of LCB usingmethods based upon solution and melt properties is facilitated.

Activation energy of flow is commonly used as an indicator of thepresence of LCB in polyethylenes as summarised in the aforementioned WO97/44371. For lower amounts of LCB, for which the global activationenergy is of the order of 28 to 45 kJ/mol, it is found that the LCB hasa strong effect upon the activation energy as measured at low test ratesie the region in which the rheology is dominated by the high molecularweight (HMW) species. Therefore, the ratio of activation energy derivedfrom the low rate data Ea(HMW) tends to exceed that derived from thehigh rate data, Ea(LMW). Hence polymers containing LCB predominantly inthe high molecular weight chains tend to show the ratio Ea(HMW)/Ea(LMW)greater than unity.

A further well established method indicating the presence of LCB is gelpermeation chromatography with on-line detection of viscosity (GPC/OLV).By combining the data from 2 detectors, the ratio g′ can be derived as afunction of molecular weight; g′ is the ratio of the measured intrinsicviscosity[η] divided by the intrinsic viscosity [η]_(liner) of a linearpolymer having the same molecular weight. In polymers containing LCB,the g′ measured at high molecular weights tends to be less than thatmeasured at low molecular weights. To quantify this effect, we have useda simple ratio g′(HMW)/g′(LMW). g′(HMW) is the weighted mean value of g′calculated for the 30% of the polymer having the highest molecularweight, while g′(LMW) is the weighted mean value of g′ calculated forthe 30% of the polymer having lowest molecular weight. For linearpolymers, g′ is equal to 1 at all molecular weights, and sog′(HMW)/g′(LMW) is also equal to 1 when there is no LCB present. Forpolymers containing LCB, g′(HMW)/g′(LMW) is less than 1. It should benoted that the g′ data can be corrected for the effect of short chainbranching (SCB). This would normally be done using a mean value of SCBcontent, the correction being applied uniformly at all molecularweights. Such a correction has not been applied here because inmeasuring the ratio g′(HMW)/g′(LMW) the same correction would apply toboth g′ values and there would be no net effect on the results reportedhere.

Another method to quantify LCB content in polyethylenes is by carbon-13Nuclear Magnetic Resonance (13C-NMR). For the low amounts of LCBobserved for polymers of the invention it is generally accepted thatthis technique can give a reliable quantification of the number of LCBpoints present in the polymer when the polymer is a homopolymer or acopolymer of ethylene and propylene or butene-1. For the purposes ofthis specification, a measurement of LCB by 13C-NMR is achieved in suchpolymers by quantification of the isolated peak at about 38.3 ppmcorresponding to the CH carbon of a tri-functional long chain branch. Atri-functional long chain branch is taken to mean a structure for whichat least the first four carbon atoms of each of the 3 chains radiatingfrom the CH branch carbon are all present as CH2 groups. Care must beexercised in making such measures to ensure that sufficient signal:noiseis obtained to quantify the resonance and that spurious LCB structuresare not generated during the sample heating by oxidation inducedfree-radical reactions.

The above described analysis of LCB by 13C-NMR is much more difficultwhen the copolymer contains hexene-1. This is because the resonancecorresponding to an LCB is very close to or overlapping that for the CHcarbon at the branch site of the n-butyl branch obtained from thiscomonomer. Unless the two CH resonances can be resolved, which isunlikely using NMR equipment currently available, LCB could only bedetermined for an ethylene/hexene-1 copolymer using the above describedtechnique if the amount of n-butyl branches was so low, in comparison tothe amount of LCB present, that it could either be ignored or a reliablesubtraction carried out on the CH resonance at about 38.3 ppm.

Using the preferred catalyst system of the present invention anethylene/butene-1 copolymer containing 6.5 wt % butene-1 has beenprepared using a continuous gas phase reactor. This polymer contained0.12 LCB/10,000 total carbons using the 13C-NMR technique describedabove. The spectrum was obtained from a 600 MHz NMR spectrometer after912,000 scans. The polymer also contained 0.25 n-butyl branches/10,000total carbons. No detectable oxidation was observed during this analysiswith a limit of detection of approximately 0.05/10,000 total carbons.

Despite a relatively low average LCB content, it would be expected thatsuch polymers would show distinctly modified rheological behaviour incomparison with truly linear polymers. If the LCB is concentrated in themolecules of higher molecular weight, as is known to be the case, thenan average value of 0.12 LCB/10,000 total carbons in the whole polymercould correspond to about 0.3 or more LCB/10,000 for molecules ofmolecular weight about one million. Hence these molecules would beexpected to contain at least 2 LCB points per molecule, equivalent to abranched structure with 5 arms. Such molecules are known to display verydifferent rheological properties to linear molecules.

The preferred polymers of the invention also show quite low amounts ofvinyl unsaturation as determined by either infra-red spectroscopy orpreferably proton NMR. For a polymer of melt index (2.16 kg) about 1,values are less than 0.05 vinyl groups per 1000 carbon atoms or even aslow as less than 0.02 vinyl groups per 1000 carbon atoms. Again, formelt index (2.16 kg) about 1, total unsaturations are also low comparedto some other metallocene polymers containing LCB, the totalunsaturations as measured by proton NMR to be the sum of vinyl,vinylidene, tri-substituted and cis+trans di-substituted internalunsaturation being in the range of less than 0.2 to 0.5 per 1000 carbonatoms. Products with higher or lower melt index, and hence lower orhigher number average molecular weights, may show respectively higher orlower terminal unsaturations, in proportion to the total number of chainends present. Hence the total unsaturations per 1000 carbon atoms areless than 17500/Mn where Mn is the number average molecular weightuncorrected for LCB and the vinyl unsaturations are less than 1750/Mn.

The comonomer present in the preferred polymers of the invention is notrandomly placed within the polymer structure. If the comonomer wasrandomly placed, it would be expected that the elution trace derivedfrom temperature rising elution fractionation (TREF) would show a singlenarrow peak, the melting endotherm as measured by differential scanningcalorimetry would also show a substantially singular and narrow peak. Itwould also be expected that little variation would be expected in eitherthe amount of comonomer measured as a function of molecular weight bytechniques such as GPC/FTIR, or the molecular weight of fractionsmeasured as a function of comonomer content by techniques such asTREF/DV. These techniques for structure determination are also describedin the aforementioned WO 97/44371, the relevant parts of which areincorporated herein by reference.

However, the comonomer may be placed in a way as to give a distinctbroadening of the TREF elution data, often with the appearance of one ortwo or even three peaks. At a polymer density of about 918 kg/m³ theTREF data typically show two main peaks, one at about 87° C. and anotherdistinct but smaller peak at about 72° C., the latter being about ⅔ ofthe height of the former. These peaks represent a heterogeneity in theamount of comonomer incorporated in the polymer chains. A third peak isoften visible at about 100° C. Without being bound by any theory thispeak is considered to be nothing other than a consequence of the factthat the polymer molecules of low comonomer content tend to crystalliseinto large chain folded crystals which melt and dissolve in the TREFexperiment in a narrow range of temperatures at about 100° C. The samepeak is very clearly visible in certain types of LLDPE polymers producedby ziegler catalysts and it is present in TREF analysis of MDPE and HDPEtype polyethylenes. Thus, without being bound by any theory, the thirdpeak at about 100° C. is more a result of the crystallisation of linearor near-linear molecules, than a feature which can be simply interpretedas representing a particular and separate polymer species.

The CDBI (Composition-Distribution Branch Index) of the polymers isbetween 55 and 75%, preferably 60 to 75%, reflecting the fact that thepolymers are neither highly homogeneous (CDBI>about 90%) nor highlyheterogeneous (CDBI<about 40%). The CDBI of a polymer is readilycalculated from techniques known in the art, such as, for example,temperature rising elution fractionation (TREF) as described, forexample, in Wild et al., Journal of Polymer Science, Polymer Phys. Ed.,Vol 20, p441 (1982), or in U.S. Pat. No. 4,798,081.

The behaviour seen in melting endotherms by DSC reflects the behaviourin TREF in that one, two or three peaks are typically seen. For examplethree peaks are often seen for the preferred polymers of density about918 kg/m³, when heated at 10° C./min. after crystallisation at the samerate. As is usual, it would be expected that the peaks seen in TREF andDSC would move to lower temperatures for polymers of lower density andto higher temperatures for polymer of higher density. The peak meltingtemperature Tp (the temperature in ° C. at which the maximum heat flowis observed during the second heating of the polymer) can beapproximated by the following expression within normal experimentalerrors:Tp=462×density−306

The amount of comonomer measured as a function of molecular weight byGPC/FTIR for the preferred polymers shows an increase as molecularweight increases. The associated parameter C_(pf) is greater than 1.1.The measurement of C_(pf) is described in WO 97/44371.

The preferred copolymers of the present invention exhibit extensionalrheological behaviour, in particular strain-hardening properties,consistent with the presence of long chain branching.

The copolymers of the present invention may suitably be prepared by useof a metallocene catalyst system comprising, for example a traditionalbisCp metallocene complex or a complex having a ‘constrained geometry’configuration together with a suitable activator.

Suitable complexes, for example, are those disclosed in WO 95/00526 thedisclosure of which is incorporated herein by reference.

Suitable activators may comprise traditional aluminoxane or boroncompounds for example borates again disclosed in the aforementioned WO95/00526.

Preferred metallocene-complexes for use in the preparation of the uniquecopolymers of the present-invention may be represented by the generalformula:

wherein:

R′ each occurrence is independently selected from hydrogen, hydrocarbyl,silyl, germyl, halo, cyano, and combinations thereof, said R′ having upto 20 nonhydrogen atoms, and optionally, two R′ groups (where R′ is nothydrogen, halo or cyano) together form a divalent derivative thereofconnected to adjacent positions of the cyclopentadienyl ring to form afused ring structure;

X is a neutral η⁴ bonded diene group having up to 30 non-hydrogen atoms,which forms a π complex with M;

Y is —O—, —S—, —NR*—, —PR*—,

M is titanium or zirconium in the +2 formal oxidation state;

Z* is SiR*₂, CR*₂, SiR*₂SIR*₂, CR*₂CR*₂, CR*═CR*, CR*₂SIR*₂, or

GeR*₂, wherein:

R* each occurrence is independently hydrogen, or a member selected fromhydrocarbyl, silyl, halogenated alkyl, halogenated aryl, andcombinations thereof, said R* having up to 10 non-hydrogen atoms, andoptionally, two R* groups from Z* (when R* is not hydrogen), or an R*group from Z* and an R* group from Y form a ring system.

Examples of suitable X groups includes-trans-η⁴-1,4-diphenyl-1,3-butadiene,s-trans-η⁴-3-methyl-1,3-pentadiene; s-trans-η⁴-2,4-hexadiene;s-trans-η⁴-1,3-pentadiene; s-trans-η⁴-1,4-ditolyl-1,3-butadiene;s-trans-η⁴-1,4-bis(trimethylsilyl)-1,3-butadiene;s-cis-η⁴-3-methyl-1,3-pentadiene; s-cis-η⁴-1,4-dibenzyl-1,3-butadiene;s-cis-η⁴-1,3-pentadiene; s-cis-η⁴-1,4-bis(trimethylsilyl)-1,3-butadiene,said s-cis diene group forming a π-complex as defined herein with themetal.

Most preferably R′ is hydrogen, methyl, ethyl, propyl, butyl, pentyl,hexyl, benzyl, or phenyl or 2 R′ groups (except hydrogen) are linkedtogether, the entire C₅R′₄ group therby being, for example, an indenyl,tetrahydroindenyl, fluorenyl, terahydrofluorenyl, or octahydrofluorenylgroup.

Highly preferred Y groups are nitrogen or phosporhus containing groupscotaining a group corresponding to the formula —N(R″)— or —P(R″)—whererin R″ is C₁₋₁₀ hydrocarbyl.

Most preferred complexes are amidosilane- or amidoalkanediyl complexes.

Most preferred complexes are those wherein M is titanium.

Specific complexes suitable for use in the preparation of the novelcopolymers of the present invention are those disclosed in theaforementioned WO 95/00526 and are incorporated herein by reference.

A particularly preferred complex for use in the preparation of the novelcopolymers of the present invention is (t-butylamido)(tetramethyl-η⁵-cyclopentadienyl) dimethylsilanetitanium-η⁴-1,3-pentadiene.

The activator may preferably be a boron compound for example a boratesuch as ammonium salts, in particular.

-   -   triethylammonium tetraphenylborate    -   triethylammonium tetraphenylborate,    -   tripropylammonium tetraphenylborate,    -   tri(n-butyl)ammonium tetraphenylborate,    -   tri(t-butyl)ammonium tetraphenylborate,    -   N,N-dimethylanilinium tetraphenylborate,    -   N,N-diethylanilinium tetraphenylborate,    -   trimethylammonium tetrakis(pentafluorophenyl) borate,    -   triethylammonium tetrakis(pentafluorophenyl) borate,    -   tripropylammonium tetrakis(pentafluorophenyl) borate,    -   tri(n-butyl)ammonium tetrakis(pentafluorophenyl) borate,    -   N,N-dimethylanilinium tetrakis(pentafluorophenyl) borate,    -   N,N-diethylanilinium tetrakis(pentafluorphenyl) borate.

Another type of activator suitable for use with the metallocenecomplexes of the present invention are the reaction products of (A)ionic compounds comprising a cation and an anion wherein the anion hasat least one substituent comprising a moiety having an active hydrogenand (B) an organometal or metalloid compound wherein the metal ormetalloid is from Groups 1-14 of the Periodic Table.

Suitable activators of this type are described in WO 98/27119 therelevant portions of which are incorporated herein by reference.

A particular preferred activator of this type is the reaction productobtained from alkylammonium tris(pentafluorophenyl) 4-(hydroxyphenyl)borates and trialkylaluminium. For example a preferred activator is thereaction product of bis(hydrogenated tallow alkyl) methyl ammonium tris(pentafluorophenyl) (4-hydroxyphenyl) borate and triethylaluminium.

The molar ratio of metallocene complex to activator employed in theprocess of the present invention may be in the range 1:10000 to 100:1. Apreferred range is from 1:5000 to 10:1 and most preferred from 1:10 to10:1.

The metallocene catalyst system suitable for use in the presentinvention is most suitably supported. Typically the support can be anorganic or inorganic inert solid. However particularly porous supportssuch as talc, inorganic oxides and resinous support materials such aspolyolefins which have well-known advantages in catalysis are preferred.Suitable inorganic oxide materials which may be used include Group 2, 1314 or 15 metal oxides such as silica, alumina, silica-alumina andmixtures thereof.

Other inorganic oxides that may be employed either alone or incombination with the silica, alumina or silica-alumina are magnesia,titania or zirconia. Other suitable support materials may be employedsuch as finely divided polyolefins such as polyethylene.

The most preferred support material for use with the supported catalystsaccording to the process of the present invention is silica. Suitablesilicas include Crosfield ES70 and Grace Davison 948 silicas.

The support material may be subjected to a heat treatment and/orchemical treatment to reduce the water content or the hydroxyl contentof the support material. Typically chemical dehydration agents arereactive metal hydrides, aluminium alkyls and halides. Prior to its usethe support material may be subjected to treatment at 100° C. to 1000°C. and preferably at 200 to 850° C. in an inert atmosphere under reducedpressure, for example, for 5 hrs.

The support material may be pretreated with an aluminium alkyl at atemperature of −20° C. to 150° C. and preferably at 20° C. to 100° C.

The pretreated support is preferably recovered before use in thepreparation of the supported catalysts of the present invention.

The copolymers of the present invention comprise copolymers of ethyleneand alpha-olefins having 3 to 10 carbon atoms. Preferred alpha olefinscomprise 1-butene, 1-hexene and 4-methyl-1-pentene. A particularlypreferred alpha olefin is 1-hexene.

Thus according to another aspect of the present invention there isprovided a process for preparing copolymers as hereinbefore describedcomprising polymerising ethylene and alpha olefins having 3 to 10 carbonatoms in the presence of a catalyst system comprising

-   -   (a) a metallocene complex of the general formula    -    wherein:    -    R′ each occurrence is independently selected from hydrogen,        hydrocarbyl, silyl, germyl, halo, cyano, and combinations        thereof, said R′ having up to 20 nonhydrogen atoms, and        optionally, two R′ groups (where R′ is not hydrogen, halo or        cyano) together form a divalent derivative thereof connected to        adjacent positions of the cyclopentadienyl ring to form a fused        ring structure;    -    X is a neutral η⁴ bonded diene group having up to 30        non-hydrogen atoms, which forms a π complex with M;    -    Y is —O—, —S—, —NR *—, —PR*—,    -    M is titanium or zirconium in the +2 formal oxidation state;    -    Z* is SiR*₂, CR*₂, SiR*₂SIR*₂, CR*₂CR*₂, CR*═CR*, CR*₂SIR*₂, or        GeR*₂, wherein:    -    R* each occurrence is independently hydrogen, or a member        selected from hydrocarbyl, silyl, halogenated alkyl, halogenated        aryl, and combinations thereof, said R* having up to 10        non-hydrogen atoms, and optionally, two R* groups from Z* (when        R* is not hydrogen), or an R* group from Z* and an R* group from        Y form a ring system,    -   (b) an activator, and    -   (c) a support.

The copolymers of the present invention are most suitably prepared inthe gas phase in particular in a continuous process operating at atemperature >60° C. and most preferably at a temperature of 75° C. orabove. The preferred process is one comprising a fluidised bed reactor.A particularly suitable gas phase process is that disclosed in EP 699213incorporated herein by reference.

When prepared by use of the preferred catalyst systems described abovethe unique copolymers of the present invention have a titanium contentin the range 0.1 to 2.0 ppm.

According to another aspect of the present invention there are provideda copolymer comprising ethylene and an alpha olefin having 3 to 10carbon atoms having

-   -   (a) a density in the range 0.900 to 0.940    -   (b) an apparent Mw/Mn of 2.5-3.0    -   (c) I₂₁/I₂ of 15 to 25, and    -   (d) a melting point of 95° C. to 135° C.

The copolymers according to the present invention may be used to preparethe full range of products normally manufactured from polyethylenecopolymer products in the density range 900 to 940 kg/m³. They may alsobe used blended with other polymers such as low density polyethylenes,linear low density polyethylenes, medium density polyethylenes, highdensity polyethylenes, plastomers and elastomers. Examples ofapplications include injection moulding, rotomoulding, extrusion intopipes, sheets, films, fibres, non-woven fabrics, cable coverings andother uses which will be known to those skilled in the art.

Thus according to another aspect of the present invention there isprovided a blend of two or more components comprising.

-   -   (a) from about 1 weight percent to about 99 weight percent of a        copolymer as hereinbefore described, and    -   (b) from about 99 weight percent to about 1 weight percent of        one or more resins that are different from component (a).

The products are particularly suitable for the production of films andsheets prepared using traditional methods well known in the art.Examples of such methods are film blowing, film casting and orientationof the partially crystallised product. The films exhibit goodprocessability, improved optical and mechanical properties and good heatsealing properties.

The films exhibit a haze ranging from 3 to 20, a dart impact >100 g andalso exhibit a low hexane extractable content of 0.1-1.5%.

Thus according to another aspect of the present invention there isprovided a film exhibiting a haze determined by ASTM D-1003 ranging from3 to 20, a dart impact measured by ASTM D-1709 of >100 g, a hexaneextractables content of 0.1-1.5%, said film comprising a copolymer ofethylene and an alpha-olefin having 3-10 carbon atoms and which has

-   -   (a) a density in the range 0.900 to 0.940    -   (b) an apparent Mw/Mn of 2-3.4    -   (c) I₂₁/I₂ from 16 to 24    -   (d) activation energy of flow from 28 to 45 kJ/mol    -   (e) a ratio Ea(HMW)/Ea(LMW) >1.1, and    -   (f) a ratio g′(HMW)/g′(LMW) from 0.85 to 0.95

Preferred films are those exhibiting a haze determined by ASTM D-1003ranging from 3 to 20, a dart impact measured by ASTM D-1709 of >100 g, ahexane extractables content of 0.1-1.5% said film comprising a copolymerof ethylene and an alpha-olefin having 3-10 carbon atoms and which has

-   -   (a) a density in the range 0.900 to 0.940    -   (b) apparent Mw/Mn in the range 2.5 to 3    -   (c) I₂₁/I₂ from-18-24    -   (d) activation energy of flow from 30 to 35 kJ/mol    -   (e) a ratio Ea(HMW)/Ea(LMW) >1.2, and    -   (f) a ratio g′(HMW)/g′(LMW) from 0.85 to 0.95

In another aspect of the present invention there is provided a filmexhibiting a haze determined by ASTM D-1003 ranging from 3 to 20, a dartimpact measured by ASTM D-1709 of >100 g, a hexane extractables contentof 0.1-1.5% said film comprising a copolymer of ethylene and analpha-olefin having 3-10 carbon atoms and which has

-   -   (a) a density in the range 0.900 to 0.940    -   (b) an apparent Mw/Mn of 2.5-3.0    -   (c) I₂₁/I₂ of 15 to 25, and    -   (d) melting point in the range 95° C. to 135° C.

The films may be suitable for a number of applications for exampleindustrial, retail, food packaging, non-food packaging and medicalapplications. Examples include films for bags, garment bags, grocerysacks, merchandise bags, self-serve bags, grocery wet pack, food wrap,pallet stretch wrap, bundling and overwrap, industrial liners, refusesacks, heavy duty bags, agricultural films, daiper liners, etc.

The films may be utilised as shrink film, cling film, stretch film,sealing film or other suitable type.

Methods of Test

Melt index (190/2.16) was measured according to ISO 1133.

Melt flow ratio (MFR) was calculated from the ratio of flow ratesdetermined according to ISO 1133 under condition (190/21.6) andcondition (190/2.16).

Density was measured using a density column according to ISO1872/1-1986, except that the melt index extrudates were not annealed butwere left to cool on a sheet of polymeric material for 30 minutes.

Apparent molecular weight distribution and associated averages,uncorrected for long chain branching, were determined by Gel PermeationChromatography using a Waters 150CV. The solvent used was 1,2,4Trichlorobenzene at 145° C., stabilised with 0.05% BHT. The nominal flowrate was 1 ml/min. Solutions of concentration 0.05 to 0.1% w/w wereprepared at 155° C. for 1.5 to 2 hours with stirring, and the nominalinjection volume was set at 250 ml. 3 Shodex AT80M/S columns were usedwith a plate count (at half height) of typically 23,000. Thedifferential refractometer detector alone was used for these studies.Calibration was achieved using broad molecular weight linearpolyethylene standards as described previously (Analysis, 1976, Vol 4 no10, p450). A correction for dispersion broadening was applied asdescribed by Hamielec (J. Appl. Polymer Sci., 14, 1519 (1970). Thiscalibration has been checked against the NIST certified polyethyleneSRM1475, the values obtained being 52,000 for Mw and 19,800 for Mn.

Molecular weight distribution and associated averages, corrected forLCB, together with g′ values as a function of MW were determined byGPC/OLV using a Waters 150CV fitted with a Viscotek 150R differentialviscometer. The Trisec version 3 software supplied by Viscotek was usedfor data treatment. SRM1475 was used as a linear reference polymer. Thesolvent used was 1,2,4 Trichlorobenzene at 142° C., stabilised with 0.2g/l Santonox R. The flow rate was nominally 1 ml/min, the injectionvolume 400 μl and the concentration injected 0.7 to 0.8 mg/ml. Thesystem was operated with 3 Shodex columns AT806MS, UT607S and AT804S,plus a Waters HR2 column. A Universal Calibration was constructed usingnarrow polystyrene standards and the Mark Houwink constants thusobtained experimentally for polystyrene were log K=−3.8283, alpha=0.687.Polyethylene Mark Houwink constants obtained from analysis of SRM1475were log K=−3.335, alpha=0.705, and these were used in the calculationsof g′.

The values for g′(HMW)/g′(LMW) were obtained from measurements of g′ vsmolecular weight obtained using the GPC/OLV system as described above.The values were calculated as the weighted mean value over the range ofinterest, as follows:${{g^{\prime}({HMW})}/{g^{\prime}({LMW})}} = {\sum\limits_{i70}^{i100}{{wi} \cdot {g_{i}^{\prime}/{\sum\limits_{i0}^{i30}{w_{i} \cdot g_{i}^{\prime}}}}}}$where for each molecular weight slice of the MWD, w_(i) is the relativeweight of polymer present, g′_(i) is the measured g′ parameter at thatmolecular weight, and i_(x) defines the slice in the MWD at which x % bywt. of the polymer has lower molecular weight.

Melting behaviour was determined by differential scanning calorimetryusing a Perkin Elmer DSC-7 instrument, following the methodologyoutlined in ASTM D3417 except that the first heating was carried out at20° C./min. The peak melting temperature was taken as the temperaturecorresponding to the maximum heat flow observed during the secondheating of the polymer at 10° C./min.

The titanium content of the copolymers was measured indirectly from ananalysis by X-ray fluorescence (XFR) of silicon content in the polymerand the known composition of the catalyst in terms of silica andreactive species supported thereon. The quantity of titanium in thecatalyst was determined by either inductively coupled plasma atomicemission spectroscopy (ICP-AES) or stomic absorption (AA).

Hexane extractable content, after extraction for 2 hours, was determinedon film samples according to ASTM-D-5227 except that the volume ofsolvent used was 300 ml.

Dart impact was measured by ASTM D1709, tear strength by ASTM D1922, andhaze by ASTM D1003.

Flow Activation Energy (Ea) Measurement

Rheological measurements were carried out on a Rheometrics RDS-2 with 25mm diameter parallel plates in the dynamic mode. Two strain sweep (SS)experiments were initially carried out to determine the linearviscoelastic strain that would generate a torque signal which is greaterthan 10% of the full scale (2000 g-cm) of the transducer over the fullfrequency (eg 0.01 to 100 rad/s) and temperature (eg 170° to 210° C.)ranges. The first SS experiment was carried out at the highest testtemperature (eg 210° C.) with a low applied frequency of 0.1 rad/s. Thistest is used to determine the sensitivity of the torque at lowfrequency. The second experiment was carried out at the lowest testtemperature (eg 170° C.) with a high applied frequency of 100 rad/s.This is to ensure that the selected applied strain is well within thelinear viscoselastic region of the polymer so that the oscillatoryrheological measurements do not induce structural changes to the polymerduring testing. This procedure was carried out for all the samples.

The bulk dynamic Theological properties (eg G′, G″ and η*) of all thepolymers were then measured at 170°, 190° and 210° C. At eachtemperature, scans were performed as a function of angular shearfrequency (from 100 to 0.01 rad/s) at a constant shear strainappropriately determined by the above procedure.

The dynamic rheological data was then analysed using the RheometricsRHIOS V4.4 Software. The following conditions were selected for thetime-temperature (t-T) superposition and the determination of the flowactivation energies (E_(a)) according to an Arrhenius equation,a_(T)=exp (E_(a)/kT), which relates the shift factor (a_(T)) to E_(a):

Rheological Parameters: G′(w), G″(w) & h*(w) Reference Temperature: 190°C. Shift Mode: 2D (ie horizontal & vertical shifts) Shift Accuracy: HighInterpolation Mode: Spline

The flow activation energy as obtained by the above t-T superpositionprocedure over the four decades of test frequency (ie 0.01 to 100 rad/s)is defined as an average flow activation energy, Ea(average), while thatover the two decades angular frequency of 0.01 to 1 rad/s as the HigherMolecular Weight flow activation energy, E_(a)(HMW) and that over thetwo decades angular frequency of 1 to 100 rad/s as the Lower MolecularWeight flow activation energy, E_(a)(LMW).

The present invention will now be further illustrated by reference tothe accompanying Examples.

Catalyst Preparation

(i) Treatment of Silica

A suspension of Grace 948 silica (13 kg, previously calcined at 250° C.for 5 hours) in 110 liters (L) of hexane was made up in a 240 L vesselunder nitrogen. 1 L of a hexane solution containing 2 g/L of Stadis 425was added and stirred at room temperature for 5 minutes. 29.1 L of a 892mmolAl/L solution of triethylaluminium (TEA) in hexane was added slowlyto the stirred suspension over 30 minutes, while maintaining thetemperature of the suspension at 30° C. The suspension was stirred for afurther 2 hours. The hexane was filtered, and the silica washed withhexane, so that the aluminium content in the final washing was less than0.5 mmol Al/liter. Finally the suspension was dried in vacuo at 60° C.to give a free flowing treated silica powder with residual solvent lessthan 0.5 wt %.

(ii) Catalyst Fabrication

All steps, unless otherwise stated, of the catalyst fabrication werecarried out at 20° C. 3 L of toluene was added to a 24 L vessel equippedwith a turbine stirrer, and stirred at 300 rpm. 5.01 L of a 9.5 wt %solution in toluene of bis(hydrogenated tallow alkyl) methyl ammoniumtris(pentafluorophenyl)(4-hydroxyphenyl)borate was added during 15minutes. Then 1.57 L of a 250 mmolAl/L solution in toluene oftriethylaluminium was added during 15 minutes and mixture stirred for 30minutes. The solution obtained was then transferred under nitrogen, withstirring during 2 hours, to an 80 L vessel containing 10 kg of the TEAtreated silica described above. 60 L of hexane was then rapidlyintroduced and mixed for 30 minutes. 1.83 kg of a 7.15 wt % solution inheptane of (t-butylamido)(tetramethyl-η⁵-cyclopentadienyl)dimethylsilanetitanium-η⁴-1,3-pentadiene was added during 15 minutes.Mixing was continued for 1 hour and 1 L of a 2 g/L hexane solution ofstadis 425 was added. The catalyst slurry was then transferred to avessel of volume 240 L and 70 L of hexane added. Excess solvent wasremoved by decantation, and a further 130 L of hexane added. Thisprocess was repeated until less than 0.2 L of toluene remained in thesolvent. 1 L of a 2 g/L hexane solution of stadis 425 was then added andthe catalyst dried under vacuum at 40° C. to a residual solvent level of1 wt %.

(iii) Polymerisation Using Continuous Fluidised Bed Reactor

EXAMPLE 1

Ethylene, 1-hexene, hydrogen and nitrogen were fed into a continuousfluidised bed reactor of diameter 45 cm. Polymer product wascontinuously removed from the reactor. Operating conditions are given inTable 1.

The results are given below in Table 2 together with typical values of aLLDPE copolymer from ethylene and 1-hexene exemplified in the literaturefrom WO 94/14855.

After degassing, the powder product withdrawn from the reactor wascompounded using a ZSK58 twin screw extruder (the additive package being1250 ppm calcium stearate, 500 ppm Irganox 1076 and 800 ppm IrgafosPEPQ). Blown film was produced at 50 kg/hr on a Reifenhauser film lineequipped with a die of diameter 150 mm and die gap 2.3 mm. The filmextrusion conditions and properties of the resultant films are alsoshown in Table 2.

EXAMPLES 2 AND 3

The catalyst of example 1 was used to produce the ethylene/1-hexenecopolymers of examples 2 and 3 using the polymerisation conditions shownin Table 1. Structural properties of these copolymers and films thereofare shown in Table 2.

EXAMPLES 4 AND 5

The procedure used in example 1 was scaled up to produce a catalyst ofbatch size approx. 75 kg. This catalyst was used to prepare copolymersin a commercial gas phase scale reactor of diameter 5 meters again usingthe polymerisation conditions shown in Table 1. Copolymers of ethyleneand 1-hexene were prepared of melt index about 1 g/10 min. and density0.918 g/cc. The structural properties of the copolymers and filmsthereof are shown in Table 2.

TABLE 1 Example 1 2 3 4 5 total pressure 17.9 18.9 19.0 19.8 20 (bar)temperature (° C.) 80 75 70 75 75 ethylene pressure 5.6 5.7 4.0 8.1 8.2(bar) H₂/C₂ ratio 0.0020 0.0025 0.0024 0.0023 0.0023 C₆/C₂ ratio 0.00400.0044 0.0036 0.0050 0.0049 production (kg/hr) 41 45 38 8700 10000

TABLE 2 Structure and film properties Property/Condition Example 1 2 3 45 LLDPE* Melt Index (dg/min) 1.04 1.57 1.2 1.3 1.07 1.0 MFR (I₂₁/I₂)20.2 21.5 22.9 19.8 21.3 18 Density (g/cc) 0.9185 0.9173 0.9198 0.91890.9184 0.918 M_(w) (uncorrected for LCB) 92,200 85,500 93,800 96,000102,600 M_(w)/M_(n) 2.33 2.5 3.2 2.7 2.6 2.6 (uncorrected for LCB)g′(HMW)/g′(LMW) 0.912 0.915 0.912 Activation energy of flow 32 32 33(kJ/mol) Ea(HMW)/Ea(LMW) 1.55 1.29 1.34 Peak melting temperature 116.4117.3 118.4 117.9 118.0 115 (° C.) CDBI (%) 73 Silicon analysis by XRF(ppm 168 180 w/w) titanium content (ppm) 0.32 0.35 dart impact(g) >1200 >1200 >1200 >1300 >1300 >800 Unsaturations by ¹H nmr cis +trans 0.05 0.04 tri 0.07 0.06 vinyl <0.02 <0.02 vinylidene <0.02 <0.02hexane extractables (wt %) 0.3 0.6 haze (%) 9.6 13.5 19.6 9.8 9 5-7gloss 58.3 44.6 34.1 54 59 MD tear strength (g/25 μm) 188 210 210 174157 370 NB. *represents published data from WO 94/14855

EXAMPLE 6

A product prepared by a similar route to example 1, and having a meltindex of 1.23 and a density of 918.2, was blown into thin film using aReifenhauser extrusion line equipped with a die of diameter 600 mm anddie gap 2.4 mm. The blow up ratio was 3:1. Both the pure product and ablend with 20% ethylene vinyl acetate (EVA) copolymer (3% VA, VF22F564supplied by BP Chemicals) were extruded. The results are given in Table3, in comparison to a commercial LLDPE, Dowlex 2045. It can be seen thatfor the examples 6a-c there is no significant processing disadvantagecompared to the LLDPE whereas the mechanical properties show aconsiderable improvement in dart impact, machine direction (MD) tear andoptical properties. In the case of film example 6c a stable extrusionwas observed at a thickness of 8 μm, indicating highly beneficial drawdown and bubble stability properties.

TABLE 3 Dowlex Dowlex Example 6(a) 6(b) 6(c) 2045 2045 Blend Pure +20%Pure Pure +20% EVA EVA Melt pressure (bar) 465 450 430 485 460 Motorload (Amps) 480 450 450 440 43075 Output (kg/hr) 339 353 275 336 340Film thickness (μm)  15  15  8  15 15 dart impact (g) >550* 365 >450*110 83 MD tear (g/25 μm) 197 106 174 150 74 Haze (%)  14  6  11  17 6Gloss  37  67  37  34 64 *measurement limited by dart hitting base ofapparatus

1. A process for preparing copolymers of ethylene and alpha olefinshaving 3 to 10 carbon atoms having (a) a density in the range 0.900 to0.940 (b) an apparent Mw/Mn of 2-3.4 (c) I₂₁/I₂ from 16 to 21.5 (d)activation energy of flow from 28 to 45 kJ/mol (e) a ratioEa(HMW)/Ea(LMW) >1.1, and (f) a ratio g′(HMW)/g′(LMW) from 0.85 to 0.95,said process carried out in the presence of a catalyst system comprising(a) a metallocene complex of the general formula

 wherein: R′ each occurrence is independently selected from hydrogen,hydrocarbyl, silyl, germyl, halo, cyano, and combinations thereof, saidR′ having up to 20 non-hydrogen atoms, and optionally, two R′ groups(where R′ is not hydrogen, halo or cyano) together form a divalentderivative thereof connected to adjacent positions of thecyclopentadienyl ring to form a fused ring structure; X is a neutral η⁴bonded diene group having up to 30 non-hydrogen atoms, which forms π awith M; Y is —O—, —S—, —NR*—, —PR* —, M is titanium or zirconium in the+2 formal oxidation state Z* is SiR*₂, CR*₂, SiR*₂SiR*₂, CR*₂CR*₂,CR*═CR*, CR*₂SiR*₂, or GeR*₂, wherein: R* each occurrence isindependently hydrogen, or a member selected from hydrocarbyl, silyl,halogenated alkyl, halogenated aryl, and combinations thereof, said R*having up to 10 non-hydrogen atoms, and optionally, two R* groups fromZ* (when R* is not hydrogen), or an R* group from Z* and an R* groupfrom Y form a ring system, (b) a borate, and (c) a support.
 2. Theprocess of claim 1 wherein the metallocene complex is a titaniumcomplex.
 3. The process of claim 2 wherein the metallocene complex is(t-butylamido) (tetramethyl-η⁵-cyclopentadienyl) dimethylsilanetitanium-η⁴-1,3-pentadiene.
 4. The process of claim 1 wherein theborate comprises the reaction product of (A) an iconic compoundcomprising a cation and an anion wherein the anion has at least onesubstituent comprising a moiety having an active hydrogen and (B) anorganometal or metalloid compound wherein the metal or metalloid is fromGroups 1-14 of the Periodic Table.
 5. The process of claim 1 wherein thesupport is silica.
 6. The process of claim 1 wherein the alpha olefin is1-hexene.
 7. The process of claim 1 wherein the process is carried outcontinuously in the gas phase.